1. Field of the Invention
In one aspect, this invention relates to a method for differentiating a noise pulse from background noise. In another aspect, this invention relates to a method and apparatus for differentiating between the noise generated by contact with underground objects and background noise. In yet another aspect, this invention relates to a method and apparatus for detecting contacts with underground objects such as utility pipelines. In yet another aspect, this invention relates to a method for evaluating the quality and condition of butt-fusion joints in plastic pipe.
2. Description of Related Art
Underground pipelines are widely used to transport a variety of fluids, including oil, natural gas, water, etc., from one place to another. Such underground systems are subject to damage from a variety of sources, both naturally occurring and man-made. For example, subsidence of the soil, local construction projects, seismic activity, and weather can all lead to defects and anomalies in the pipeline. Also, harsh environments can cause pipelines to move gradually over time, leading to defects, cracks, leaks, bumps, and other anomalies, within the interior of the pipeline.
Continuous monitoring of long pipelines, whether for seismic events or impacts occurring during excavation in proximity to the pipeline, is not a simple task. Damage to pipelines can be detected in a variety of ways including detection of the substance that escapes from the pipeline as the result of the damage, pressure drops in the pipeline, and impacts on the pipeline. And, when construction equipment, for example, a backhoe, strikes an underground utility pipeline, an acoustic signal is generated that propagates along the length of the pipeline.
There are several systems and methods known to those skilled in the art for monitoring the condition of underground pipelines. Acoustic monitoring of an underground pipeline may be carried out by a variety of acoustic sensors/detectors, such as geophones, accelerometers and the like. However, one problem with the use of acoustic means for monitoring underground pipelines is noise, both background and sensor noise, in the output signal from these means, which noise may partially or possibly completely mask the signal of interest, thereby precluding detection of the pipeline condition. For example, while sounds associated with impacts on a pipeline can be transmitted through the pipeline and detected at substantial distances from the point of contact via such highly sensitive acoustic sensors, the high sensitivity of such sensors can produce or result in a significant number of false calls arising from sources such as nearby traffic, passing pedestrians, low-level ground movement, and weather conditions such as thunder. Accordingly, to better enable the use of acoustic means for monitoring underground pipelines, one alternative is to substantially reduce or, if possible, eliminate the noise in the output signals from the acoustic sensors/detectors. Another alternative is to utilize the characteristics of the noise generated by the impact to distinguish the impact noise from the background noise.